Difference between revisions of "Tutorials:Pointers"

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: WORD : ''int64/long''
 
: WORD : ''int64/long''
  
In programs and programming simply using integers, floating point values, and strings really isn't feasible with complex objects. So the concept of an object in memory was seen as a must. This is where pointers come in. They simply point to an object in memory, hence the name.
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In programs and programming simply using integers, floating point values really isn't feasible with complex objects. So the concept of an object in memory was seen as a must. This is where pointers come in. They simply point to an object in memory, hence the name. Even strings are implemented with pointers to the series of characters in memory, though most high-level languages don't make you aware of that fact.
  
Technically strings are pointers to character arrays, that end with a null byte (0x0). In the [https://en.wikipedia.org/wiki/ANSI_C ANSI C] there is no string type just character arrays.
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In the [https://en.wikipedia.org/wiki/ANSI_C ANSI C] there is no string type just character arrays, and they'd better have a 0x0 / NUL / NULL byte after all the characters if you want to use them with any standard library function!
  
 
==== Objects in memory ====
 
==== Objects in memory ====

Revision as of 22:09, 5 February 2018


Make sure to understand value types or read this first: Value types


Pointers are integers who's size is the base word size of the process and store an address in that process. That is in a 16 bit process a pointer is a WORD (16 bit), in a 32 bit process a pointer is a DWORD (32 bit), and in a 64 but process a pointer is a QWORD (64 bit).

16 bit
WORD : int16/short
32 bit
WORD : int32/int
64 bit
WORD : int64/long

In programs and programming simply using integers, floating point values really isn't feasible with complex objects. So the concept of an object in memory was seen as a must. This is where pointers come in. They simply point to an object in memory, hence the name. Even strings are implemented with pointers to the series of characters in memory, though most high-level languages don't make you aware of that fact.

In the ANSI C there is no string type just character arrays, and they'd better have a 0x0 / NUL / NULL byte after all the characters if you want to use them with any standard library function!

Objects in memory

Now let's say we have some code that declares a player object and its setup like this:

  • Player : object
    • Name : string
    • Health : integer
    • Coins : integer
    • Coordinates : object
      • X : float
      • Z : float
      • Y : float
    • Inventory : array - Array of item objects, having the item and item count.


So in a 32 bit process in memory the player object could get assembled some thing like this:

  • Process.exe+123ABC : pointer : DWORD - Player base.
    • [Process.exe+123ABC]+10 : pointer : DWORD - Pointer to where the Name string is stored in memory.
      • [[Process.exe+123ABC]+10]+4 : string : 256 bytes - The Name value, as a null (0x0) ended string.
    • [Process.exe+123ABC]+14 : integer : DWORD - Health value.
    • [Process.exe+123ABC]+18 : integer : DWORD - Coins value.
    • [Process.exe+123ABC]+1C : pointer : DWORD - Pointer to where the Coordinates object is stored in memory.
      • [[Process.exe+123ABC]+20]+10 : float : DWORD - X coordinate.
      • [[Process.exe+123ABC]+20]+14 : float : DWORD - Z coordinate.
      • [[Process.exe+123ABC]+20]+18 : float : DWORD - Y coordinate.
    • [Process.exe+123ABC]+24 : pointer : DWORD - Pointer to where the Inventory array starts in memory.
      • [[Process.exe+123ABC]+24]+XX*4 : pointer : DWORD - Pointer to where the inventory array item number XX is stored in memory.
        • [[[Process.exe+123ABC]+24]+XX*4]+4 : integer : DWORD - The inventory item Count value.
        • [[[Process.exe+123ABC]+24]+XX*4]+8 : pointer : DWORD - Pointer to where item object is stored in memory.


And in a 64 bit process in memory the player object could get assembled some thing like this:

  • Process.exe+123ABC : pointer : QWORD - Player base.
    • [Process.exe+123ABC]+10 : pointer : QWORD - Pointer to where the Name string is stored in memory.
      • [[Process.exe+123ABC]+10]+8 : string : 256 bytes - The Name value, as a null (0x0) ended string.
    • [Process.exe+123ABC]+18 : integer : DWORD - Health value.
    • [Process.exe+123ABC]+1C : integer : DWORD - Coins value.
    • [Process.exe+123ABC]+20 : pointer : QWORD - Pointer to where the Coordinates object is stored in memory.
      • [[Process.exe+123ABC]+20]+10 : float : DWORD - X coordinate.
      • [[Process.exe+123ABC]+20]+14 : float : DWORD - Z coordinate.
      • [[Process.exe+123ABC]+20]+18 : float : DWORD - Y coordinate.
    • [Process.exe+123ABC]+28 : pointer : QWORD - Pointer to where the Inventory array starts in memory.
      • [[Process.exe+123ABC]+28]+XX*8 : pointer : QWORD - Pointer to where the inventory array item number XX is stored in memory.
        • [[[Process.exe+123ABC]+28]+XX*8]+4 : integer : DWORD - The inventory item Count value.
        • [[[Process.exe+123ABC]+28]+XX*8]+8 : pointer : DWORD - Pointer to where item object is stored in memory.


But if we had an Actor object that held all the values, and then a Player object that inherits from Actor, a Player object could get assembled some thing like this:

  • Process.exe+123ABC : pointer : DWORD - Player base.
    • [Process.exe+123ABC]+4 : pointer : DWORD - Actor base.
      • [[Process.exe+123ABC]+4]+10 : pointer : DWORD - Pointer to where the Name string is stored in memory.
        • [[[Process.exe+123ABC]+4]+10]+4 : string : 256 bytes - The Name value, as a null (0x0) ended string.
      • [[Process.exe+123ABC]+4]+14 : integer : DWORD - Health value.
      • [[Process.exe+123ABC]+4]+18 : integer : DWORD - Coins value.
      • ...


And the more complex the object structure the more complex the pointer structure.


Example of multi-level pointers

Check out step 8 of the Cheat Engine Tutorial for an example of multi-level pointers.


See also

External links